1. Field of the Invention
The invention relates to a filtering arrangement for relay protection devices.
2. The Prior Art
High-voltage lines can be protected by means of remote protection arrangements which requires information as to the voltage and current on the power line to make possible a selective disconnection of the faulty line. In case of high system voltages, practical and economical reasons have necessitated the use of capacitive voltage transformers (CVT) for measuring the voltage. Unfortunately, these transformers give rise to a low-frequency or aperiodic transient which is superimposed on the measuring signal. This makes itself especially felt in the case of large voltage reductions. From the voltage and the current from the measuring transformers signals are derived, which then undergo phase and amplitude comparison in the remote protection arrangement. Because of the transients there is a risk of incorrect measuring if no corrective measures are taken. A common corrective measure is to place a filter between the measuring transformer and the remote protection arrangement, and to block the measuring relay of the remote protection arrangement during the transient and building-up periods of the filter, which often results in long times of operation for the remote protection arrangement.